diff --git a/src/python/flowmetal/parser.py b/src/python/flowmetal/parser.py
index 3843a88..6ab72b5 100644
--- a/src/python/flowmetal/parser.py
+++ b/src/python/flowmetal/parser.py
@@ -272,32 +272,55 @@ class Parser(SexpParser):
     def parse_sqlist(cls, f: PosTrackingBufferedReader):
         return cls.parse_delimeted(f, "[", "]", lambda *args: ListToken(*args, ListType.SQUARE))
 
+    # FIXME (arrdem 2020-07-18):
+    #  Break this apart into middleware or composable features somehow?
     @classmethod
     def handle_symbol(cls, buff, pos):
-        # Parsing integers
-        if m := re.fullmatch(r"[+-]?\d[\d_]*", buff):
-            return IntegerToken(int(buff.replace("_", "")), buff, pos)
+        def _sign(m, idx):
+            if m.group(idx) == '-':
+                return -1
+            else:
+                return 1
 
         # Parsing integers with bases
-        elif m := re.fullmatch(r"(\d+)r([a-z0-9_]+)", buff):
-            return IntegerToken(int(m.group(2).replace("_", "")), int(m.group(1)), buff, pos)
+        if m := re.fullmatch(r"([+-]?)(\d+)r([a-z0-9_]+)", buff):
+            return IntegerToken(
+                _sign(m, 1) * int(m.group(3).replace("_", ""),
+                                  int(m.group(2))),
+                buff,
+                pos,
+            )
+
+        # Parsing hex numbers
+        if m := re.fullmatch(r"([+-]?)0[xX]([A-Fa-f0-9_]*)", buff):
+            val = m.group(2).replace("_", "")
+            return IntegerToken(_sign(m, 1) * int(val, 16), buff, pos)
+
+        # Parsing octal numbers
+        if m := re.fullmatch(r"([+-]?)0([\d_]*)", buff):
+            val = m.group(2).replace("_", "")
+            return IntegerToken(_sign(m, 1) * int(val, 8), buff, pos)
+
+        # Parsing integers
+        if m := re.fullmatch(r"([+-]?)\d[\d_]*", buff):
+            return IntegerToken(int(buff.replace("_", "")), buff, pos)
 
         # Parsing fractions
-        elif m := re.fullmatch(r"([+-]?\d[\d_]*)/(\d[\d_]*)", buff):
+        if m := re.fullmatch(r"([+-]?)(\d[\d_]*)/(\d[\d_]*)", buff):
             return FractionToken(
                 Fraction(
-                    int(m.group(1).replace("_", "")),
-                    int(m.group(2).replace("_", ""))),
+                    int(m.group(2).replace("_", "")),
+                    int(m.group(3).replace("_", ""))),
                 buff,
                 pos,
             )
 
         # Parsing floats
-        elif re.fullmatch(r"[+-]?\d[\d_]*(\.\d[\d_]*)?(e[+-]?\d[\d_]*)?", buff):
+        if re.fullmatch(r"([+-]?)\d[\d_]*(\.\d[\d_]*)?(e[+-]?\d[\d_]*)?", buff):
             return FloatToken(float(buff), buff, pos)
 
-        else:
-            return SymbolToken(buff, buff, pos)
+        # Default behavior
+        return SymbolToken(buff, buff, pos)
 
     @classmethod
     def parse_symbol(cls, f: PosTrackingBufferedReader):
@@ -331,6 +354,7 @@ class Parser(SexpParser):
             buff = str(rtb)
             return CommentToken(buff, buff, pos)
 
+
 ## Parsing interface
 def parses(buff: str,
            parser: SexpParser = Parser,
diff --git a/test/python/flowmetal/test_parser.py b/test/python/flowmetal/test_parser.py
index bac2344..11fda87 100644
--- a/test/python/flowmetal/test_parser.py
+++ b/test/python/flowmetal/test_parser.py
@@ -20,10 +20,32 @@ def test_parse_list():
     ('2', 2),
     ('103', 103),
     ('504', 504),
+    # Sign prefixes
     ('-1', -1),
     ('+1', +1),
+    # Underscores as whitespace
+    ('1_000_000', 1e6),
     ('+1_000', 1000),
     ('-1_000', -1000),
+    # Variable base
+    ('2r1', 1),
+    ('2r10', 2),
+    ('2r100', 4),
+    ('2r101', 5),
+    ('+2r10', 2),
+    ('-2r10', -2),
+    # Octal
+    ('00', 0),
+    ('01', 1),
+    ('010', 8),
+    ('+010', 8),
+    ('-010', -8),
+    # Hex
+    ('0x0', 0),
+    ('0xF', 15),
+    ('0x10', 16),
+    ('+0x10', 16),
+    ('-0x10', -16),
 ])
 def test_parse_num(txt, val):
     """Some trivial cases of parsing numbers."""